In turbine nozzles conventional impingement cooling inserts are disposed inside nozzle cavities to augment heat transfer coefficients and increase cooling of the airfoil walls.
As shown in FIGS. 1–2, insert 10 is disposed within nozzle 11. The dashed line in FIG. 1 denotes the location of a metering plate. Conventional cooling inserts, shown in FIG. 3, that are mounted inside the airfoil cavity, as opposed to the outside nozzle wall, typically involve the use of stiff collars 30 on the ends of the inserts 10. As a result, the nozzle ribs 31 must be machined on both sides to create proper tight tolerance interfaces for the inserts.
These ribs are typical of most nozzle designs and are primarily for structural purposes. In an open and closed circuit cooling design it is desirable to seal the cooling insert along the entire perimeter. This seal weld or braze involves a weld along two sides to the nozzle sidewall, with the other two sides being a weld to the nozzle internal ribs. Typically the ends of the ribs need to be machined to achieve a proper interface for welding or brazing.
The provision of stiff collar 30 around insert 10 is to make the interface mechanically sound. However, stiff collar 30 makes it difficult to manufacture and assemble cooling insert 10 into the nozzle cavity. Also the necessary machining of rib 31 is difficult due to the casting tolerances of internal rib 31. Accordingly, there is a need for a better interface to the internal ribs.
In addition, cooling inserts that are mounted on internal airfoil cavities to “flashribs” also have stiff collars on the cooling inserts and the nozzle interface must be machined on both sides of the internal ribs. This makes for a complex assembly as close tolerance fits are required to braze or Laser or Electron Beam weld the inserts to the nozzle. Much scrap and rework often must be produced due to the complex interface. In addition, the part life is reduced due to leakage across the joint and weak joints that create cooling loss and cracking.